I agree with what others have said about John needing to see Rodney's committment.

Also, I DO think you have to accept that John is a top and allow him to express that. You accept that someone might want to receive pain and you do have to accept that someone might want to hand it out. Not in the sense that they want to hurt, but as part of sexual pleasure for both top and sub. John knows that Rodney is a sub and he's finding out that Rodney actually likes the intensity of pleasure/pain - and John likes drawing those responses out of his sub. It's very unfair to John to assume he's just enjoying inflicting pain any more than you'd judge Rodney for wanting to receive punishment.